Adoptive cell immunotherapy with immune checkpoint inhibitors has shown clinical promise. Unfortunately, despite optimizations of treatments, relapse-free survival rates still range between 17-21% in most metastatic solid tumors. This occurs via various tumor-induced abnormalities including immunosuppression and emergence of immune escape tumor variants. Tumor growth can induce immunosuppression by multiple mechanisms. We identified a novel mechanism of immunosuppression wherein tumor interferes with the host hematopoietic Notch system that is critical for lymphocyte differentiation and function. Our studies in solid tumor models demonstrate that lymphocyte teamwork, specifically between CD8+T cell and NK cell effectors, is essential to eradicate tumor cells. However, immunosuppressive chronic inflammation in the tumor microenvironment hinders this phenomenon. Thus, strategies that can reverse Notch dysfunction in lymphocytes and restore the CD8+T?NK crosstalk are critical for effective tumor eradication and durable remission. Facilitated by SCORE funding support, we found that proteasome inhibitor bortezomib modulates Notch signaling in lymphocytes and enhances their antitumor activity. Additionally, our data also indicate that bortezomib may augment CD8+T and NK cell crosstalk. Based on these data, we hypothesize that bortezomib overcomes tumor-induced immunosuppression by enhancing the antitumor adaptive and innate immune effector crosstalk via modulation of the hematopoietic Notch system. In this competing renewal application, we propose to extend our studies to the next level whereby we can advance our basic insights into CD8+T?NK crosstalk and Notch-mediated lymphocyte mechanisms into a preclinical therapeutic setting. We will test our hypothesis by addressing how bortezomib can facilitate the CD8+T?NK crosstalk (Aim 1), and Notch- dependent mechanisms affecting antitumor lymphocyte cross-talk (Aim 2). Investigations will include genetic approaches based on the use of unique cell type-specific Notch ligand conditional knockout mice that we have generated to clearly define the roles of dendritic cell-bound ligands in antitumor CD8+T?NK functional crosstalk. In Aim 3, we propose to evaluate the therapeutic impact of bortezomib-mediated enhancement of Notch signaling and CD8+T?NK crosstalk on tumor rejection and relapse-free survival. We will use an inducible lung cancer model carrying EGFR mutations. We will integrate bortezomib and adoptive CD8+T and NK cell transfers along with EGFR-targeted therapy and evaluate the impact of this combinatorial regimen on tumor remission and relapse-free survival. Altogether, the studies proposed in this SC1 renewal application will unravel novel mechanisms underlying lymphocyte antitumor crosstalk, and will provide innovative insight into modulation of Notch regulatory lymphocyte mechanisms using bortezomib for translation into clinically relevant therapeutics in advanced-stage, mutant, or resistant lung cancer. In addition, it would enhance the cancer immunotherapy training program and PI?s capacity to transition to non-SCORE extramural funding support.